Such a damping means is described in United Kingdom Patent Specification GB1251468A and the corresponding German Patent Specification DE1952620A, in which (as shown in FIG. 17 of that specification) the phasing means comprise pins or dowels acting between the hubs of the two friction wheels, with each of these pins engaging circumferentially, with a clearance, with the common hub.
The predamper has a cap which is force fitted onto an axial projection of the hub of one of the friction wheels. It is thus not possible to carry out any separate testing on the predamper, which is however necessary in some cases. In addition, one of the friction wheels is located axially on the common hub by means of a ring which is engaged in a groove machined in the teeth of the common hub. The machining of this groove can produce undesirable burrs.
All this complicates manufacture and increases the number of components.
It might be thought that an intermediate indexing ring could be used, meshing with a clearance, by means of teeth, with the common hub, and meshing without clearance with the hubs of the friction wheels. However, this requires a large number of broaching or milling, and machining operations, and imposes limitations on the size of the common hub.